It is known from the prior art to reshape plastic preforms into plastic receptacles in blowing stations. For that purpose the plastic receptacles are heated before the actual blowing process in order to be expanded in this way.
Various heating devices and ovens, respectively, are known from the prior art which heat such plastic preforms. Different procedures are known from the prior art for heating the preforms. Firstly microwave ovens are known which use microwaves to heat the plastic preforms. Also however infrared ovens are known which heat the receptacles using thermal radiation.
In previously conventional processes, the plastic preform is irradiated with IR radiators (infrared) with a continuous Planckian radiation spectrum. The advantage here is the high efficiency of the radiation source which is almost 100%. One disadvantage of this procedure is that the preform does not absorb all wavelengths evenly. For example, there are wavelengths in which untreated polyethylene terephthalate (PET) is virtually transparent, such as for example at a wavelength of approximately 1000 nm. At other wavelengths, the plastic preform, where made from PET, is substantially totally impermeable such as for example at 2300 nm, and in further other ranges it is partly transparent.
One disadvantage of the said IR radiators is that they have a very high energy requirement. Secondly however not all wavelengths of the radiator can be used in the same way.
DE 10 2006 015853 A1 discloses a heating method for plastics and other materials with an infrared device. At least two radiators are provided which are used on the basis of one and the same functional ceramic with a selective infrared, wherein their emission spectrums largely correspond with the absorption spectrums of the materials to be heated. In this case therefore the aim is for as much radiation as possible to be absorbed by the plastic preforms. This however leads in some cases to heating occurring only on the surface of the plastic preforms and not in the inner zones of the material.
DE 20 2008 005252 U1 discloses only a lamp device for a radiant heating of preforms. A reflector is provided which, in relation to a peripheral direction of an axis running through the radiation source, extends peripherally over an angle which is greater than 200°.
DE 38 23 670 A1 describes a method for heating preforms with at least one heater emitting radiation, the radiation of which is aligned at least also in the direction towards the preform to be heated. The preform is irradiated with a radiation which heats its wall in the inner zone as strongly as in the outer zone.
The present invention is based on the object of making the ovens known from the prior art more energy-efficient. Furthermore, an innovative energy-saving method is provided for preform heating, in particular for the stretch-blow moulding process in drinks bottles.